1. Field of the Invention
The present invention relates to a sheet feeding apparatus, and more particularly it relates to a sheet feeding apparatus used for a sheet feeding system of an image reading equipment such as a scanner, facsimile or the like.
2. Related Background Art
An image reading equipment using a conventional sheet feeding apparatus of this kind is shown in FIG. 1.
In FIG. 1, an image reading equipment 100 includes a first feeding means 105 comprising an entrance roller 102, a feed roller 103 and a separating roller 104, and a second feeding means 107 comprising a feed conveying roller against which a reading means 106 is urged, these first and second feeding means being disposed along an original feeding direction (through which an original 101 as a sheet is fed) at upstream and down stream sides, respectively. Incidentally, the reference numeral 108 denotes an original detecting sensor arranged between the first feeding means 105 and the second feeding means 107.
In a sheet feeding apparatus 109 so constructed, the original 101 is fed out toward the downstream side by rotating the feed roller 103 in a anticlockwise direction, and the a leading end of the original 101 is abutted against a contacting portion a between a contact glass S of an image sensor of contact type (constituting the reading means 106) and the second feeding means 107, and then the original is further fed to form a loop in the original for correcting the skew feed of the original, and thereafter, the reading and ejection of the original is effected by conveying the original by rotating the second feeding means 107 in an clockwise direction. During this operation, the separating roller 104 is always driven in an clockwise direction through a torque limiter (not shown) to prevent the double-feed of the originals.
However, in the conventional sheet feeding mechanism utilizing the friction of the rollers, the loop in the original (sheet) can often not be formed in accordance with the conditions of the material of the original, the coefficient of friction of the rollers and the change thereof, the urging force acting on the friction roller and/or the distance between the friction roller and an sheet outlet.
Further, in such sheet feeding mechanism, the feed roller 103 incorporates a one-way clutch therein for transmitting a driving force of the feed roller to only one direction (original feeding direction, during the feeding of the original). However, conventional one-way clutches transmit a little driving force even in a reverse direction (to which the driving force should not be transmitted) (i.e., original returning direction, during the conveying of the original for reading). Further, the separating roller 104 is always driven through the torque limiter in the original returning direction.
Consequently, before the conveying roller of the second feeding means 107 is driven in the original feeding direction to pinch the leading end of the original and to convey the original for the reading thereof, the feed roller 103 and/or separating roller 104 often causes the leading end of the original to move back from a position where the leading end has been abutted against the contacting portion a, thus arising the erroneous feeding or poor feeding.
In order to prevent such poor feeding, a technique in which, when the original is fed by the rotation of the feed roller 103, the conveying roller 107 is also driven, and the feed roller 103 is stopped after the conveying roller 107 has pinched the leading end of the original has been proposed. However, in this case, there arose a problem that the skew feed of the original occurred because the posture of the original could not be corrected before the conveying of the original.